JP3472992B2 - How to connect electrodes - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting electrodes using an adhesive, and more particularly to a method for connecting high density electrodes composed of a semiconductor chip and a circuit board.

[0002]

2. Description of the Related Art In recent years, as a method of connecting high density electrodes, compared to conventional rigid connection using solder or eutectic,
The connection method using an adhesive, which is capable of soft connection and capable of relieving thermal stress, is becoming popular.

This method includes a method in which a conductive material is interposed between electrodes by a liquid adhesive or a film-like material containing a predetermined amount of a conductive material such as particles, or an insulating material containing no conductive material and having no conductivity. There is known a method of adhering and fixing a conductive material disposed between electrodes facing each other or on an electrode with a conductive adhesive in a contact state.

At the time of this connection, a press method is generally used in which a heating plate such as an infrared heater or a heating die heated by a pulse current is pressure-bonded. At this time, a silicone rubber sheet, Teflon, or the like is placed between the electrode substrate and the heating plate. It has been practiced to place a thin piece made of the above polymer films and thermocompression-bond it.

Since the thin piece body has a cushioning property when thermocompression-bonded by the above-mentioned method, when the electrode substrate is flexible such as polyimide or polyester, it is possible to absorb variations in the electrode height at the time of collective connection. Further, it is possible to prevent the adhesive from flowing out from contaminating the hot platen and also to protect the substrate from damage.

[0006]

However, when a thin piece made of a silicone rubber sheet or a polymer film is placed as described above, the substrate moves relatively freely until the connection with the adhesive is completed. Therefore, although it is possible to absorb the variation in the height of the electrode, there is a problem in that the surface direction of the electrode is misaligned, and in particular, the misalignment with the relatively opposing electrode is misaligned with the recent progress in miniaturization of the electrode. Has occurred.

Further, since these thin pieces have a low thermal conductivity, it takes a long time for the adhesive to reach the connection temperature, and there is a drawback that the productivity is poor. Further, since these thin pieces are insulators, there is a problem that electronic parts such as a semiconductor chip may be broken due to static electricity generated during connection work.

Therefore, the present invention has been made to solve the above-mentioned problems, and it is difficult to cause a gap between the electrodes facing each other.
Another object of the present invention is to provide an electrode connecting method which is excellent in productivity and measures against static electricity.

[0009]

In order to achieve the above-mentioned object, the invention according to claim 1 is such that an adhesive is interposed between an electrode provided on a substrate and an electrode facing each other, and a pressure plate is used for pressure bonding. In the electrode connecting method described above, a flexible metal foil is placed between at least one of the substrates and the heating plate, and then thermocompression bonding is performed.

According to a second aspect of the present invention, in the first aspect, the flexible metal foil has a thickness of 500 μm.
m or less, and is characterized by being any of aluminum, copper, iron, and alloys containing 50% by weight or more of these.

FIG. 1 is a sectional view showing the construction of a connecting method according to an embodiment of the present invention.

The substrate 1 used in the present invention is a general insulating substrate of semiconductor chips such as silicone, gallium / arsenic, etc., glass, ceramics, insulating metal, glass / epoxy composite, plastic, etc.

The electrodes 2 provided on the insulating substrate include bumps and pads of semiconductor chips and a printed circuit board having protruding electrodes such as copper foil on the insulating substrate.

These electrodes 2 are electrodes 2'that face each other.
It is preferable that at least one of them protrudes from the substrate surface because it is easy to obtain contact with the electrodes, but other opposing electrodes are obtained by, for example, a thin film method or an additive method, so-called planar electrodes, bumpless semiconductor chips, etc. It may be a concave electrode as in the case. The electrodes of the bumpless semiconductor chips are formed in a concave shape of about several microns from the surface insulating layer, but in this case as well, the electrodes facing each other can be applied by projecting from the substrate surface (for example, transfer bumps or the like).

The adhesive 3 is an adhesive or a film-like material containing a predetermined amount of conductive particles as a conductive material, which interposes a conductive material between electrodes, or does not contain a conductive material and has no conductivity. It is also possible to more efficiently obtain contact between the electrodes facing each other by adding conductive particles that adhere and fix the electrodes facing each other with an insulating adhesive in a contact state. In this case, it should be noted that the particle size is made smaller than the distance between the adjacent electrodes, and the addition amount is set to 20% by volume or less, preferably 15% by volume or less so as not to short-circuit with the adjacent electrodes.

As the adhesive 3, a thermoplastic material or a material having adhesiveness which is curable by heat or light can be widely applied. These are excellent in heat resistance and moisture resistance after connection,
Of these, application of a curable material is preferable. In particular, an epoxy adhesive is preferably applicable because it can be cured for a short time, has good workability in connection, and has excellent adhesiveness due to its molecular structure.

The above-mentioned epoxy-based adhesive is generally composed of, for example, a high molecular weight epoxy, a solid epoxy and a liquid epoxy as a main component, and a curing agent, a catalyst, a coupling agent, a filler and the like are added.

As the conductive particles, Au, Ag, Ni, C are used.
There are metal particles such as u, W, Sb, Sn, and solder, carbon, etc., and these conductive particles are used as the core material, or cores made of non-conductive glass, ceramics, polymers such as plastics, etc. The material may be formed by coating a conductive layer made of the above-mentioned material.

Further, it is also possible to use insulating coated particles obtained by coating the above-mentioned conductive particles with an insulating layer, and to use both conductive particles and insulating particles in combination.

Among these conductive particles, those having a conductive layer formed on a hot-melting metal such as solder or a polymer core material such as plastic are heated and pressed or are deformable by pressurization. In addition, the contact area with the circuit is increased and the contact reliability is improved, which is preferable. In particular, when a polymer is used as a core, a connecting member that can easily cope with variations in the thickness and flatness of the electrodes 2 and 2'can be obtained, which is particularly preferable.

As the flexible metal foil 4, various kinds of flexible metal foils can be applied. 180 with a radius of curvature of 10 mm or less
It is said to have flexibility when it can be bent to a certain degree. With this flexibility, damage to the connection body can be prevented, and pressing can be performed with the folded foil sandwiched. The flexible metal foil 4 has a thickness of 500 μm or less, and is as thin as possible for handling, for example, a thickness of 2 to 200 μm.
About m is preferable, but a more preferable thickness is 5 to 50 μm.

The material of the flexible metal foil 4 may be aluminum, copper, iron, or an alloy containing 50% by weight or more of these. It is preferable that these surfaces are as smooth as possible, and it is preferable that they have conductivity in order to prevent electrostatic breakdown during connection.

The aluminum foil used as the flexible metal foil 4 is preferably an aluminum foil having an aluminum content of 90% or more, preferably 95% or more, from the viewpoint of spreadability and conductivity. These are JIS, H4160, 4170 and Z
4170 is particularly preferred because it is easy to obtain and relatively inexpensive because it is easily available.

The copper foil may be an electrolytic foil or a rolled foil, but a rolled foil having flexibility and a smooth surface is preferable because it is easily available. Zinc, tin, lead, silver, nickel and the like are known as copper alloys. Also, in the case of magnetic metals such as iron, they can be set on a heating plate by magnetization.

The flexible metal foil 4 used in the present invention is
It is preferable that it exists in contact with both the surface plate 6 and the heating plate 5, but at least it must exist in contact with the substrate 1 on the heating plate 5 side.

Although other sheets may be present on the heating plate 5 side of the flexible metal foil 4, it is preferable not to improve the thermal conductivity. The hot platen 5 may be not only one but also the platen 6 side.

In the connection using the adhesive 3, the adhesive 3 is formed between the electrode 2 provided on the substrate 1 and the electrode 2'which faces the electrode 2, and both electrodes 2 and 2'are aligned to each other. The flexible metal foil 4 is placed between the one substrate 1 and the heating plate 5 and thermocompression bonded. At this time, it is preferable that the adhesive 3 is connected at a poise of 1000 poise or less due to low viscosity due to heating, since the contact between the electrodes or between the electrodes and the conductive particles is good.

[0028]

In the present invention, the flexible metal foil is placed between one of the substrates and the heating plate and thermocompression bonded. Therefore, the flexible metal foil, which is a metal, has a higher elastic modulus than a rubber sheet or a polymer film, and since it does not synchronize with the deformation of the substrate, it is unlikely to be displaced from the electrodes facing each other, and has a large thermal conductivity. Therefore, it is possible for the adhesive to reach the connection temperature in a short time, and the productivity is improved.

Further, the flexible metal foil has the flexibility,
Because of its high elastic modulus and high thermal conductivity,
Even if the thickness of itself is small, it has a strength that can be handled, so that damage to the connection body can be prevented, and since a heat source can be effectively used, resource saving and cost reduction can be achieved.

Further, since it is a conductor, static electricity generated during connection work can be eliminated by grounding it via, for example, a thermal bonding device, so that electrostatic damage to electronic parts such as semiconductor chips does not occur.

Further, since the flexible metal foil is resistant to organic solvents, it is easy to wash and can be reused after being contaminated.

[0032]

EXAMPLES The present invention will now be described in detail based on examples, but the present invention is not limited to the examples described below.

First, first and second embodiments of the present invention will be described.

An FPC circuit board having a width of 30 mm and having a copper circuit having a height of 18 μm on a polyimide film (a circuit pitch is 100 μm, electrodes of a parallel circuit having an electrode width of 50 μm),
Indium oxide thickness 0.2 μm on glass 1.1 mm
It was connected to a glass electrode having a thin film circuit of (ITO, surface resistance 20 Ω / □).

The connection was made by connecting the glass electrode to Anisorum AC-7.
144 (Anisotropic conductive film, resolution 14 lines / mm, containing epoxy conductive thermosetting adhesive conductive particles plated on plastic of particle size 5 μm, trade name manufactured by Hitachi Chemical Co., Ltd.) with a width of 1.5 mm After attaching and peeling the separator, the FPC circuit board and both electrodes are aligned, and then two sun foils (manufactured by Sun Aluminum Industry Co., Ltd.,
It is sandwiched between aluminum foil with a thickness of 15 microns and can be bent 180 degrees with a radius of curvature of 2 mm), 160 ° C, 30 kgf
/ Mm ² , It heated for 15 seconds. At this time, when the temperature was set to 250 ° C. with a thermocompression bonding apparatus (manufactured by Hitachi Chemical Co., Ltd., trade name AC-S3000C, the heating plate is grounded with an earth wire) having a constant heating type heating plate on the top, the temperature starts to rise. Two seconds later, the adhesive temperature reached 160 ° C. (First embodiment) Therefore, in comparison with 15 seconds of the first embodiment, a shorter time of 5
The second embodiment was connected even in seconds. Further, when the elongation amount of the FPC after connection was measured by a three-dimensional measuring device (manufactured by Mitoyo Co., Ltd., trade name AE-100), the maximum was 5 μm in both Examples. Further, in both Examples, there was almost no change in the connection resistance in the reliability evaluation of the connected body (85% RH, after 1000 hours), which was good. In the above two examples, household aluminum foil was used, so it was inexpensive and easy to replace when the aluminum foil was contaminated.

Comparative examples 1 and 2 of the above two examples are shown below.

Comparative Examples 1 and 2 are the case where the aluminum foil is not used (Comparative Example 1) and the case where the conventional silicone rubber having a thickness of 250 μm is used (Comparative Example 2). Other conditions are the same as those of the first embodiment. Was measured.

The temperature rising rate and elongation amount of Comparative Example 1 were the same as those of the first example, but the adhesive flowed out to the hot plate and was cured, and it was very difficult to take out the connected body. Further, since it took a long time to clean the hot platen, continuous work was difficult.

In the case of Comparative Example 2, it took 16 seconds to reach 160 ° C. and the maximum elongation was 47 μm. In this case, the reliability of the connection body was lower than that of the first embodiment due to the small overlapping area of the opposing electrodes and the insufficient heat capacity during connection.

Next, a third embodiment of the present invention will be described.

In the third embodiment, instead of the FPC, an IC chip (2 × 10 mm, height 0.5 mm, 50 μm square called bump around the four sides, height 20 μm square, height 20 μm) is used.
Although 200 gold electrodes of m were formed), other conditions were the same as those in the first embodiment. The ITO electrode on the glass side was changed so as to correspond to the size of the bump electrode of the IC chip.

In the above embodiment, the displacement of the bump electrode is 5 μm.
m was less than or equal to m, no electrostatic damage to the IC chip was observed, and the reliability of the connected body was good. Due to the flexibility of the aluminum foil, no chipping or cracking of the end surface of the IC chip was observed.

Next, the fourth embodiment and comparative example 3 will be described.

The fourth embodiment is Anisorum AC-7144.
No conductive particles of the adhesive were added, but the other conditions were the same as in the third embodiment. In this case as well, it was possible to conduct electricity by the contact of both electrodes, and the subsequent peeling and connection with an adhesive were also good, and a connection with excellent reliability was obtained by adhesive fixing.

In Comparative Example 3, the silicone rubber of Comparative Example 2 was used between the hot platen and the silicone rubber.

In the fourth embodiment, the displacement of the bump electrodes was 5 μm or less, no electrostatic breakdown of the IC chip was observed, and the reliability of the connection body was good. The contact condition between the bump electrode and the substrate was uniform, and the curing of the bump flattening by uniform pressure was also obtained.

On the other hand, in Comparative Example 3, the displacement of the bump electrode is 2
It was 0 μm, and electrostatic breakdown of the IC chip was observed. In addition, the contact between the bump electrode and the substrate was found to be uneven.

Next, a fifth embodiment will be described.

The fifth embodiment uses aluminum foil instead of
Rolled copper foil (35 μm thick double-sided glossy smooth product, radius of curvature 2
However, the other conditions were the same as those in the first embodiment.

In the fifth embodiment, the rate of temperature rise, the amount of elongation, and the reliability were as good as those in the first embodiment. Further, copper foil, which is a general material in the electronic industry, can be used, and it is easily available.

[0051]

As described above, according to the present invention, the gap between the electrodes facing each other when bonding is less likely to occur,
Since the thermal conductivity is high, it is possible for the adhesive to reach the connection temperature in a short time and the productivity is improved.The flexible metal foil has flexibility and has a high elastic modulus and thermal conductivity. Since it has a high property, damage to the connection body can be prevented and the heat source can be effectively used, so that resource saving and cost reduction can be achieved. Further, since it is a conductor, static electricity generated during connection work can be eliminated by grounding, so that it is possible to provide a connection method that is also excellent against static electricity.

[Brief description of drawings]

FIG. 1 is a configuration cross-sectional view showing a connection method.

[Explanation of symbols]

1,1 'substrate 2, 2'electrode 3 adhesive 4 Flexible metal foil 5 hot plate 6 surface plate

Front page continuation (72) Inventor Kazuhiro Isaka 1500 Ogawa, Shimodate, Ibaraki Hitachi Chemical Co., Ltd. Shimodate Research Laboratory (72) Inventor Kayoshi Kojima 1500 Ogawa, Shimodate, Ibaraki Hitachi Shimodate In the laboratory (72) Kyohisa Ota, 1500 Ogawa, Ogawa, Shimodate, Ibaraki Hitachi Chemical Co., Ltd. in the Shimodate laboratory (56) Reference JP-A-5-218634 (JP, A) (58) Fields investigated (58) Int.Cl. ⁷ , DB name) H01R 43/00 H05K 3/32

Claims (2)

(57) [Claims] 1. A method of connecting electrodes, in which an electrode provided on a substrate and an electrode facing each other are pressure-bonded to each other with an adhesive agent interposed therebetween, in a method of connecting the electrodes to at least one of the substrate and the heating plate. A method for connecting electrodes, comprising placing a flexible metal foil and then thermocompression bonding. 2. The flexible metal foil has a thickness of 500.
2. The method for connecting electrodes according to claim 1, wherein the electrode has a thickness of less than or equal to .mu.m and is aluminum, copper, iron, or an alloy containing 50% by weight or more thereof.